Time travel paradox solved

[Bouncing Zabaglione Bros.]

How would it do that? Isn't the navigation system fused into rock 5 metres underground along with the time-travellers?

Something has to turn up first to make sure the traveller will end up in the right place. I guess you could beam some sort of ship into orbit around the Earth, then have it send the coordinates back in time to the time-machine in the present. That still doesn't solve the potential problem of suddenly appearing and having all the air that was in your place get mixed up with your body.
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No it doesn't. If you're going to theorise about "magic" technology like time travel, then you can easily make it "magic enough" to get you to the right place in space as well as time. If you can travel through the timelines of probability, why not be able to sense them coming as you move towards them? Sense the actions you need to take to get you to where you need to go without landing in a rock.

Cars and planes navigate themselves via their pilots and internal systems, why wouldn't a time & space machine? It just as likely as being able to throw some kind of beacon through millions of miles of space and thousands of years and have it be able to signal to the other end across all that distance.

 

[Nathan]

No it doesn't. If you're going to theorise about "magic" technology like time travel, then you can easily make it "magic enough" to get you to the right place in space as well as time. If you can travel through the timelines of probability, why not be able to sense them coming as you move towards them? Sense the actions you need to take to get you to where you need to go without landing in a rock.

Cars and planes navigate themselves via their pilots and internal systems, why wouldn't a time & space machine? It just as likely as being able to throw some kind of beacon through millions of miles of space and thousands of years and have it be able to signal to the other end across all that distance.

Except that the context of this discussion is about predicting where things will be in the future so you can arrive there safely, which implies that time travelling is not a continuous journey from point A to point B-in-the-future. You are assuming it is continuous, so you do not need to predict anything because you could just react to the changes as they happened.

Since we know assumption is the mother of all fuck ups, I feel confident that not assuming time travel is continuous is the safest course of action.

 

[Frank]

Wouldn't it be a bit of a bummer, that we might only be able to travel through time like that if the Earth would be at the exact same location as it is now? Or otherwise use a very fast spaceship to cover the distance?

That might take all the everyday fun out of it, but it sounds much more realistic.

 

[Nathan]

Wouldn't it be a bit of a bummer, that we might only be able to travel through time like that if the Earth would be at the exact same location as it is now? Or otherwise use a very fast spaceship to cover the distance?

That might take all the everyday fun out of it, but it sounds much more realistic.

I think a DeLorean is fast enough too.

 

[OpenGL guy]

Wouldn't it be a bit of a bummer, that we might only be able to travel through time like that if the Earth would be at the exact same location as it is now? Or otherwise use a very fast spaceship to cover the distance?

That might take all the everyday fun out of it, but it sounds much more realistic.

I think a DeLorean is fast enough too.

Don't forget the gigawatts!

 

[Bigus Dickus]

OGLguy,

AFAIK, all of the current semi-sane physical theories of time travel have the restriction that travel is restricted between two times in which the "device" existed. The "device" could be a wormhole, big honking cylinder, some exotic form of matter, or any of the other only mostly loony concepts from the fringe of science.

For any time travel method in which we actively create the conditions that allow the travel (such as actively open a wormhole, make a funky machine, etc.), the above stipulation carries the implication that we can only travel to times in the past after the point at which we created those conditions. You can't build a time machine today and then travel back to last year... you can only travel back to today from other times in the past. Even if it is unlikely that time travel is possible, I believe it to be even more unlikely that a natural phenomenon will have already created the necessary conditions. Perhaps we'll get lucky and find black holes to be a natural source though?

This carries the logical consequence that navigating man-made time travel will be a breeze, as we know precisely where we will "land." It will be wherever our "machine" was on the day we travel to it. So navigation into the past poses no real concerns, so long as you keep good records!

Now, navigating into the future is the more sticky issue. I think the only way to travel forward outside what we consider the normal flow of time (which includes relativistic effects) would be if a static time (time slice) model of the universe is true, in which all "events" both past and present already exist and similarity between time slices (including similarity of neural states for humans) is responsible for our perception of a flow of time. In that case, traveling into the past again becomes sticky as time slices past and future become equivalent, and knowing where the "device" is in the "past" is no more guaranteed than knowing where it is in the "future." i.e., going into the past would land you in an alternate "timeline" in which the device might for some reason happen to be buried at that instant.

I sleep better believing time is not discrete and static, and that past travel is possible if intractable, and limit my fantasies to forward travel through reletavistic effects and rearward travel to rather recent times.

 

[OpenGL guy]

This carries the logical consequence that navigating man-made time travel will be a breeze, as we know precisely where we will "land." It will be wherever our "machine" was on the day we travel to it. So navigation into the past poses no real concerns, so long as you keep good records!

I don't think it's so simple. As I stated earlier, we can only speak about where things are right now, not where things were last year, or even 5 minutes ago. This is because we don't know the velocities and accelerations we're undergoing (or were undergoing) (Nathan's N-body problem).

 

[Bigus Dickus]

Hmm... I don't think I was very clear in my explanation.

The reason you know where you will "land" in the past is that you know it is the location of the "time traveling device" that you constructed. Your travel is bound to this location because of the limitation that backwards travel can only occur within the times when the device existed. What I didn't make clear is that the device should have defined spatial locations for the starting and destination points. Different "devices" have different definitions for these points, but they are not arbitrary. I do not believe there is any theory in which you can simultaneously travel in temporal and spatial coordinates. I agree that this seems odd, but the temporal travel is locked to the device assisting the travel, and that device has a clearly defined location in both time frames.

So as long as you are careful to keep good records, you should know where the device is and whether things are "clear" for the destination time. The reason you have these records is because you presumably created the device and know its past very well. If we were to find that black holes could function as natural devices, then obviously we wouldn't know the past that well, but in that case you are in a craft in essentially empty space, presumably with the ability to cover vast distances, so your destination location wouldn't appear to be quite so crucial as materializing five feet below the ground.

This should hold true even in a bizarre static discrete time universe. There the apparent flow of time would be governed by the similarity between two given time slices. If the device did not exist in both starting and destination slices, then there would not be the required similarity to allow travel (apparent? ugh...) between them.

 

[blakjedi]

Now, navigating into the future is the more sticky issue. I think the only way to travel forward outside what we consider the normal flow of time (which includes relativistic effects) would be if a static time (time slice) model of the universe is true, in which all "events" both past and present already exist and similarity between time slices (including similarity of neural states for humans) is responsible for our perception of a flow of time. In that case, traveling into the past again becomes sticky as time slices past and future become equivalent, and knowing where the "device" is in the "past" is no more guaranteed than knowing where it is in the "future."

Exactly. But the real problem is whether time is discrete or analog and whether or not there is any such thing other than "now".

The universe may not keep a record as it moves and evolves of what it did... by the same token because the future hasnt happened yet from our point of view well we just cant say...

 

[sunscar]

My god people have seriously over-complicated time travel...

 

[K.I.L.E.R]

So when will we get some applications?

 

[nutball]

So when will we get some applications?

Never.

 

[Bouncing Zabaglione Bros.]

So when will we get some applications?

Never.

Time travel into the future is fairly simple. You just get on a spaceship, get it up to near the speed of light, and then do a big circle back to earth. A few subjective years might have passed on board the spaceship, but hundreds or thousands will have passed back on earth. It's a one way journey.

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

 

[nutball]

Time travel into the future is fairly simple. You just get on a spaceship, get it up to near the speed of light, and then do a big circle back to earth. A few subjective years might have passed on board the spaceship, but hundreds or thousands will have passed back on earth. It's a one way journey.

One way time travel is of limited application though, wouldn't you agree?

Stephen Baxter (a physics professer who writes SF) has got around that problem by making a wormhole, and putting one end of it on the above spaceship. The wormhole goes on the subjective trip lasting a few years a the speed of light while thousands of years pass on earth. When you want to go back in time, you just step back through the wormhole which now connects the future back to the past as well as two points in space.

Wormholes, schwirmholes. Nice mathematical mind-games, but do they have any basis in physical reality?

 

[Bouncing Zabaglione Bros.]

One way time travel is of limited application though, wouldn't you agree?

Depends what your application is, wouldn't you agree?

Wormholes, schwirmholes. Nice mathematical mind-games, but do they have any basis in physical reality?

Yes. They fit within our current physics theories as being possible. They don't break the rules like a lot of other fictional constructs such as people travelling back signficant distances in time and changing the present by changing the past.

 

[nutball]

Yes. They fit within our current physics theories as being possible.

In what sense? In the sense that they are valid solutions to the current accepted mathematical formulations?

 

[V3]

If light can travel at speed of light and arrive here for us to observe, I think we can also arrive at the same place.

 

[Bouncing Zabaglione Bros.]

Yes. They fit within our current physics theories as being possible.

In what sense? In the sense that they are valid solutions to the current accepted mathematical formulations?

In the sense that they don't break the laws of currently accepted theories like other fictional constructs, at least as far as they have been theorised:

http://www.hypography.com/topics/wormholes.cfm
http://www.pbs.org/wnet/hawking/strange/html/wormhole.html
http://casa.colorado.edu/~ajsh/schww.html
http://spaceinfo.jaxa.jp/note/shikumi/e/shi104_warmhole_e.html?CFID=1065281&CFTOKEN=22676686
http://news.bbc.co.uk/1/hi/sci/tech/4564477.stm

You can do more Googling yourself if you like.

 

[nutball]

In the sense that they don't break the laws of currently accepted theories like other fictional constructs, at least as far as they have been theorised:

<snip>

You can do more Googling yourself if you like.

I'm familiar with the concept of wormholes, I think what I'm trying to do is sound out whether or not you're a physicist!

Point is that they are valid solutions to currently accepted theories (as represented by some maths), that's not the same thing as saying that the are physically possible. Mathematical possibility != physical possibility.

As a trivial example, F = ma as a mathematical formula is quite happy if m is a negative number. Most reasonable physicists accept however that in the real Universe (certainly the one to which Newton's Law apply) negative mass is non-physical.

Whilst Newton's Laws are regarded as somewhat old hat these days, the point remains that not all solutions of the equations underlying the theories necessarily have a physical manifestation in the real world.

 

[Bouncing Zabaglione Bros.]

Point is that they are valid solutions to currently accepted theories (as represented by some maths), that's not the same thing as saying that the are physically possible. Mathematical possibility != physical possibility.

I'd agree, and you should be able to tell that from the language I used in my posts. I never said wormholes were possible, only that wormhole theory does not break current physics theories the way other things do (like time travel changing the past). I even refer to them as in the same sentence as "other fictional constructs".